Rowe Sam, Kabera Fidele, Dufour Simon, Godden Sandra, Roy Jean-Philippe, Nydam Daryl
Sydney School of Veterinary Science, The University of Sydney, Camden, New South Wales 2570, Australia; Department of Veterinary Population Medicine, University of Minnesota, St. Paul 55108.
Département de pathologie et microbiologie, Faculté de médecine vétérinaire, Université de Montréal, Saint-Hyacinthe, Quebec, Canada J2S 2M2; Mastitis Network, Saint-Hyacinthe, Quebec, Canada J2S 2M2.
J Dairy Sci. 2023 Mar;106(3):1953-1967. doi: 10.3168/jds.2022-22547. Epub 2023 Jan 16.
Antibiotic stewardship on dairy farms can be heightened through the implementation of selective dry-cow therapy (SDCT). However, some producers are concerned that this practice may be related to poor udder health outcomes in cows with high milk production at the time of dry-off. The objective of this study was to evaluate if the effect of culture-guided SDCT (Cult-SDCT) and algorithm-guided SDCT (Alg-SDCT) on dry-period intramammary infection (IMI) dynamics and postcalving udder health and performance [when compared with blanket dry-cow therapy (BDCT)] varied according to milk production level before dry-off. Data were compiled from clinical trials conducted in the United States and Canada that compared Cult-SDCT and Alg-SDCT to a positive control, i.e., BDCT. In those trials, cows were enrolled 1-2 d before dry-off, randomized to their dry-cow therapy strategy and followed until 120 d in milk of the subsequent lactation. The number of cows and quarters in the final data set were 1,485 and 5,097, respectively. Measured outcomes included quarter-level antibiotic use at dry-off, quarter-level IMI prevalence after calving, quarter-level dry-period IMI cure risk, quarter-level dry-period new IMI risk, cow-level clinical mastitis and removal from the herd during 1-120 d in milk, and somatic cell count and milk yield during 1-120 DIM. The primary objective of analysis was to investigate if the effect of Cult-SDCT and Alg-SDCT on these outcomes, when compared with BDCT, varied according to milk production level before dry-off. To do this, each cow was classified as having low, mid or high production, based on her milk yield tertile group at the most recent herd test before enrollment (low: <23.7 kg/d, mid: 23.7 to 30.4 kg/d, and high >30.4 kg/d). Multivariable generalized estimating equations were used to estimate risk differences and differences in means, and Cox regression was used to estimate hazard ratios. For Cult-SDCT, the proportion of quarters treated with dry-cow antibiotics within each milk production level were 40.7% (low), 41.7% (mid) and 47.2% (high). For Alg-SDCT, the proportions were 60.6% (low), 38.7% (mid), and 35.1% (high). Measures of udder health were not markedly different when comparing Cult-SDCT to BDCT and Alg-SDCT to BDCT. This was consistently observed in low, mid and high producing cows. In conclusion, the findings from this study indicate that Cult-SDCT and Alg-SDCT can be successfully implemented in cows of all milk production levels.
通过实施选择性干奶期治疗（SDCT），可加强奶牛场的抗生素管理。然而，一些养殖户担心这种做法可能与干奶期时高产奶牛的乳房健康状况不佳有关。本研究的目的是评估与全面干奶期治疗（BDCT）相比，培养物引导的SDCT（Cult-SDCT）和算法引导的SDCT（Alg-SDCT）对干奶期乳房内感染（IMI）动态变化以及产犊后乳房健康和生产性能的影响是否因干奶前的产奶水平而异。数据来自美国和加拿大进行的临床试验，这些试验将Cult-SDCT和Alg-SDCT与阳性对照即BDCT进行了比较。在这些试验中，奶牛在干奶前1 - 2天入组，随机分配到其干奶期治疗策略，并跟踪至随后泌乳期的产奶120天。最终数据集中奶牛和乳腺区的数量分别为1485头和5097个。测量的结果包括干奶期乳腺区抗生素使用情况、产犊后乳腺区IMI患病率、干奶期乳腺区IMI治愈风险、干奶期乳腺区新IMI风险、奶牛水平的临床乳腺炎以及产奶1 - 120天内被淘汰出牛群的情况，以及产奶1 - 120天内的体细胞计数和产奶量。分析的主要目的是研究与BDCT相比，Cult-SDCT和Alg-SDCT对这些结果的影响是否因干奶前的产奶水平而异。为此，根据入组前最近一次牛群检测时的产奶量三分位数组，将每头奶牛分为低产、中产或高产（低产：<23.7千克/天，中产：23.7至30.4千克/天，高产：>30.4千克/天）。使用多变量广义估计方程来估计风险差异和均值差异，并使用Cox回归来估计风险比。对于Cult-SDCT，每个产奶水平下接受干奶牛抗生素治疗的乳腺区比例分别为40.7%（低产）、41.7%（中产）和47.2%（高产）。对于Alg-SDCT，这些比例分别为60.6%（低产）、38.7%（中产）和35.1%（高产）。将Cult-SDCT与BDCT以及Alg-SDCT与BDCT进行比较时，乳房健康指标没有明显差异。在低产、中产和高产奶牛中均一致观察到这一点。总之，本研究结果表明，Cult-SDCT和Alg-SDCT可在所有产奶水平的奶牛中成功实施。
